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i I. I. I I I I I I., f, I I I I I I I' I I EXECUTIVE SUMMARY The Rio Grande has a history of flooding which dates back to 1869. More recently. flood conditions occurred in 1985. 1986. and 1987 ,in the Alamosa area. Only a successful flood fight and flood mitigation measures prevented substantial damage within the community. Flood damages in the' vicinity of Alamosa prior to the channel Clearing and levee rehabilitation projects for the city and county was estimated to be $1. 047.700 per year. This vulnerability to floods not only robbed the local economy but also inhibited the chances for sound economic development. Government agencies were becoming reluctant to sponsor any more projects in the 100-year floodplain. Almost the entire developed area is SUbject to shallow 100-year flooding from the Rio Grande. Hot temperatures and an unusually heavy late snowpack in the upper reaches of the Rio Grande basin combined to cause unusually rapid runoff in June 1985. 1986. and 1987. A peak discharge of 4.420 was measured at the Alamosa gage on June 9. 1985. This magnitude flood can be expected to occur about once every 8 years on the average. Although failure did not occur. the existing levee system proved to be structurally unsound in several areas. These levees were constructed in a piecemeal fashion during the 1940's and do not meet current federal levee cri teria. It was estimated that floods greater than about a 25-year magnitude (7.000 cfs) would flank the levees and flood the entire city. Flood damages in 1985 amounted to approximately $601.474 to the county and $187.772 to the city. Denial of a Community Development Block Grant application for low income housing re-habilitation in the floodplain and flood damages in 1985 caused the local elected officials to rethink their community development priori ties. By pooling their resources in a coordinated effort. the City of Alamosa and Alamosa County worked together to develop a strategy to mitigate the flood hazard. Reducing vulnerabili ty to flood losses was viewed as a fundamental step towards continued improvement in the local economy. A formal request was made to the Colorado Water Conservation Board to serve as project coordinator to formulate a flood control project for A1amosa and vicinity. A technical advisory committee was formed to assist with the technical aspects of project formulation and funding. In September 1985. Muller Engineering Company Inc. under contract to prepare a Feasibility Study formulation and cost. was placed for project vi